The present invention relates generally to pneumatic tires, more specifically to radial ply pneumatic tires, and still more specifically to radial ply pneumatic aircraft tires.
The operating conditions for tires on the European Air Bus may be considered as an example of what aircraft tires must endure The main wheels on the aircraft support around 18,000 kilograms each at the aircraft's take-off weight, or about four times the maximum load of a truck tire of comparable size. During take-off the air bus attains a speed of about 350 kilometers per hour. As the air bus lifts off the ground, the main tires are spinning at about 1,600 revolutions per minute, and the nose-wheel tires are spinning at about 1,900 revolutions per minute. Upon landing the air bus makes contact with the runway at speeds of about 240 kilometers per hour and the rotational velocity of the tires rapidly increases from zero to about 1,100 revolutions per minute. During this process, the tire-surface speed is much less than the aircraft speed, resulting in substantial abrasion of the tire tread and heat generation within the tire. Also, reverse thrust of the engines during landing can increase the aircraft nose-wheel loading by up to 100 percent.
The Air Bus operating conditions for tires are severe, but those under which military aircraft tires must operate are even more demanding. For example, a French military aircraft known as a Mirage has tires on its main wheels that are comparable in size to the tires specified for a large automobile. However, on a Mirage the main tires support a static load of about 7,200 kilograms each. At take-off the smaller nose-wheel tires are spinning at about 5,400 revolutions per minute.
While this invention is particularly directed to the solution of problems that are most severe in aircraft tire applications, it is applicable in general to other pneumatic tires either which are of radial ply construction or which employ one or more reinforcement plies having parallel cords or cables of the same or nearly the same orientation. Typically such tires are of radial construction, which means that the parallel cords or cables form an angle between about 70.degree. and 90.degree. with respect to the mid-circumferential plane of the tire. In most radial ply tires, the angle of the cords or cables in each bead-to-bead reinforcement ply is in the range from 80.degree. to 90.degree. with respect to the mid-circumferential plane, and usually is near 90.degree..
Pneumatic tires having radial reinforcement plies as mentioned above most frequently have only one or two reinforcement plies extending between the tire beads. In many cases, a single reinforcement ply is used and it has parallel cords or cables at an angle of 90.degree. with respect to the mid-circumferential plane of the tire. Under severe loading, such as occurs with aircraft tires, the parallel cords or cables in the shoulder regions of the tire tend to spread apart during deflection of the tire casing. Even if more than one radial ply is used, there is a tendency for the cords or cables to separate under loading and this weakens the tire in the regions between the cords or cables.
It is not unusual in pneumatic tires to place a "chipper" in the bead region of the tire to provide additional stiffness to its lower sidewall portion. The chipper is a reinforcement that typically extends from the mid-sidewall region to a region near the bead (around which it may be wrapped) and is located on the outer side of the bead. In some cases, a plurality of chippers are used to provide a stiffness variation desired in the lower sidewall or bead area of a particular tire.
The liner of a pneumatic tire is an impermeable elastomeric material positioned inside the tire to prevent air loss. Butyl and other materials typically used as liners have had the characteristic of extruding into regions between the parallel cords or cables in the carcass reinforcement ply or plies, particularly those of radial ply tires. This condition is aggravated where only a single main carcass reinforcement ply is used. A known method for preventing the extrusion of the liner material into the region between the parallel cords or cables of a carcass reinforcement ply is to add to the liner a second elastomeric "barrier" ply extending between the beads of the tire. This barrier elastomeric ply may be precured, either in whole or on one of its surfaces only, to prevent the liner material from being extruded into the region between the cords or cables of the reinforcement ply. Alternatively, a separate reinforcement material can be utilized as is illustrated in U.S. Pat. No. 3,165,138 issued Jan. 12, 1965 to J G Manchetti and H B Hindin. In the patent to Manchetti and Hindin, there is described a radial tire having a casing with a single full reinforcement ply extending from bead-to-bead. A barrier material is positioned in the casing to prevent the liner from extruding into the region between the radial cords or cables of the carcass. The barrier material is shown having a bias-cut fabric material that has a free end, an end which is unanchored, to permit the fabric material to remain free during shaping of the tire.
Other patents of interest with respect to the present invention include U.S. Pat. No. 4,445,560, issued May 1, 1984 to Jacques Musy, and U.S. Pat. No. 4,258,773, issued Mar. 31, 1981 to Michele R. Saint-Michel. These patents are directed to radial carcass aircraft tires having one or more radial plies extending from bead-to-bead and having a belt assembly positioned in the crown region of the tires to provide circumferential reinforcement.